Use a Stated Transfer Fraction

Supplied materials

• Use the supplied fictional observations or model. Paper and pencil are optional; spoken answers are welcome. No equipment or real experiment is needed.

Learn the idea

A food-chain diagram does not tell transfer amounts unless numbers or rules are added. Our fictional accounting model starts with 1,000 energy units stored in grass growth. Exactly one tenth becomes rabbit growth, and exactly one tenth of that becomes fox growth. These are supplied model fractions, not a universal ten-percent rule for all ecosystems.

Energy absent from the next organism’s growth has other destinations. Organisms transfer thermal energy through life processes, and energy can remain in uneaten material, waste, or other organisms. This calculation tracks growth available along one route, not all ecosystem transfers. Distinguish the 1,000 stored grass units from all sunlight arriving at the grass.

1. Label grass growth with 1,000 units.
2. Multiply by 1/10 to obtain rabbit growth.
3. Multiply the rabbit value by 1/10 for fox growth.
4. Explain why the smaller growth values do not mean energy vanished.

Check your reasoning

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Take it further

Change only the rabbit-to-fox growth fraction to one fifth. Starting at 600, rabbit growth remains 60 and fox growth becomes 60 × 1/5 = 12 units.

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